1. Field of the Invention
Example embodiments relate to an expandable, pipe plug assembly that may be used on a riser pipe of a Boiling Water Reactor (BWR) jet pump assembly. The pipe plug assembly may be used to secure a pipe collar or bracket to the riser pipe for riser pipe repair. The pipe plug assembly includes a pipe plug that acts as a wedge to expand bushing sections to assure a tight fit within a hole that may be match drilled to ensure a uniform hole exists in the riser pipe as well as the collar or bracket that may be fashioned to the riser pipe. A thin shape of the bushing sections and the existence of narrow gaps between bushing sections mitigate leakage to acceptable levels especially in flooded environments such as the annulus region where the riser pipe exists with the Boiling Water Reactor (BWR).
2. Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In the BWR, hollow tubular jet pumps of a jet pump assembly are positioned within the shroud annulus. The jet pump assembly accepts energized water from outside of the reactor recirculation system and provides the required reactor core water flow to the reactor via diffusers. The formation of minute cracks in the riser pipe may sometimes require repair, which may require the fashioning of a collar or bracket to the outer surface of the riser pipe.
Conventionally, fashioning of a collar or bracket to the rounded surface of the riser pipe may cause complications, especially in the case where access to the inside diameter of the riser pipe is unavailable. Specifically, outer surfaces of a plug that may be used to secure the collar or bracket to the circumferential surface of the riser pipe may be out of alignment with holes drilled in the collar, the bracket, or the riser pipe itself, causing vibration and leakage. Additionally, conventional plugs may not provide radial forces (pressure) to ensure a tight fit between a plug and the collar and/or riser pipe holes.
Alternative to the example embodiments described below, tapered holes with tapered plugs have been considered to securely fashion a collar or bracket to the riser pipe. However, lack of control during electrical discharge machining (“EDM”) burns may not guarantee tight tolerances in a tapered angle, resulting in a weak connection between a collar and riser pipe, leakage, as well as deformation or cracking of components.